A liquid crystal display or the like has an image-forming mechanism in which polarizing elements are essentially placed on both sides of the liquid crystal cell, and generally, polarizing plates are attached as the polarizing elements. Besides polarizing plates, various optical elements for improving display quality are used in a liquid crystal panel. For example, there are used a retardation plate for preventing discoloration, a viewing angle expansion film for improving the viewing angle of the liquid crystal display, and a brightness enhancement film for enhancing the contrast of the display. These films are generically called optical films.
When such optical films are attached to a liquid crystal cell, a pressure-sensitive adhesive is generally used. In the process of bonding an optical film and a liquid crystal cell or optical films together, a pressure-sensitive adhesive is generally used to bond the materials together so that optical loss can be reduced. In such a case, a pressure-sensitive adhesive optical film including an optical film and a pressure-sensitive adhesive layer previously formed on one side of the optical film from a pressure-sensitive adhesive composition is generally used, because it has some advantages such as no need for a drying process to fix the optical film.
In a conventional technique, when the process of bonding a pressure-sensitive adhesive optical film to the surface of a liquid crystal cell suffers from bonding misalignment or trapping of foreign matter, which may cause a failure in liquid crystal display, the bonded pressure-sensitive adhesive optical film is peeled off and replaced with a new one, which is bonded again to the surface of the liquid crystal cell. However, as the size of liquid crystal displays increases or as the thickness of liquid crystal cells decreases, it is becoming difficult to peel off pressure-sensitive adhesive optical films. In particular, a large force is necessary to peel off a pressure-sensitive adhesive layer with a high adhesive strength, which may cause problems such as poor workability, display quality degradation due to changes in liquid crystal cell gap, and damage to the liquid crystal cell. In order to keep the manufacturing cost low, pressure-sensitive adhesive optical films are also required to be capable of being peeled off and reused and to have such reworkability that they can be peeled off with no adhesive deposit.
Methods proposed to solve the above problems include a method that includes peeling an optical film, while softening or melting the pressure-sensitive adhesive with an electrically heated wire or a heated slicer being inserted between a liquid crystal panel and the optical film (Patent Documents 1 and 2), and a method that includes making incisions in an optical film placed on a liquid crystal panel to divide the optical film into fragments and peeling off the fragments (Patent Document 3).
Another proposed method includes immersing, in an alkaline solution, a display material to which a transparent film is bonded with a pressure-sensitive adhesive interposed therebetween, and then peeling the transparent film and the pressure-sensitive adhesive from the display material (Patent Document 4).
There are further proposed a method that includes bonding a peeling sheet to the optical member to be peeled off and peeling the optical member together with the peeling sheet (Patent Document 5) and a method including bonding a pressure-sensitive adhesive tape to a polarizing plate and peeling the polarizing plate with the pressure-sensitive adhesive tape (Patent Document 6).
There are further proposed a method of removing a polarizing plate or the like from a glass substrate by immersion in concentrated sulfuric acid (Patent Document 7), a method of peeling off a polarizing plate by dissolving and removing a pressure-sensitive adhesive with a solvent such as acetone or trichloroethylene (Patent Document 8), a method of dissolving and removing a polarizing plate with a solvent capable of solubilizing the polarizing plate (Patent Document 9), and a method of peeling a pressure-sensitive adhesive optical film in the presence of a liquid at the peel interface between the substrate and the pressure-sensitive adhesive layer of the pressure-sensitive adhesive optical film (Patent Document 10).
However, these methods involve a laborious work such as insertion of a peeling tool between a liquid crystal panel and an optical film or cutting only an optical film placed on a liquid crystal panel. These methods also have a problem such as a large amount of an adhesive deposit left on the liquid crystal panel or damage to the liquid crystal panel from a solvent.